Various nutritional elements are necessary for plants to grow. For example, nitrogen, phosphorus and potassium are known as three macronutrients contained in a fertilizer. Further, as minerals, Ca, Mg, Fe, S, B, Mn, Cu, Zn, Mo, Cl, Si, Na and the like are necessary. These nutritional components such as nitrogen, phosphorus and potassium or minerals are applied in a form of a base fertilizer or an additional fertilizer, or a liquid fertilizer is diluted and the resulting liquid is applied by soil drench or foliar spraying. Further, in plant tissue culture such as production of mericlone plants, they are added as medium components. These components are essential and necessary for plants to grow. However, even if they are applied at a concentration not lower than a certain concentration, they cannot contribute to the improvement of the growth and yield of plants any more.
However, it is an important object in the agricultural production to try to increase the yield by promoting the growth of agricultural crops thereby to increase the crop yield per unit area or to shorten the cultivation period, and various plant growth regulators required for the above object have been developed and used. The plant growth regulators typified by gibberellin, auxin and the like are used for regulating growth and morphogenetic reaction such as germination, rooting, elongation, flowering and fruiting, however, the action of these substances is diverse and complicated, and their use is limited. In order to solve such a problem, a technique in which a foliar spraying agent using an oligosaccharide or a liquid fertilizer containing a sugar, a mineral, an amino acid, a seaweed extract or a microbial fermentation extract is sprayed onto leaves or fertilization is carried out in the form of a solution is known, however, it is not satisfactory in terms of the effect for practical purpose at present.
Further, in the conventional plant growth regulators, an action of promoting the growth of plants are regarded as important, and it is not intended to target an action of inhibiting the growth of plants except for herbicides and the like. However, a technique of appropriately inhibiting the growth of plants in a field of storage of seedlings in preparation for permanent planting or prolongation of life of ornamental plants or the like has been demanded.
On the other hand, in the agricultural production, measures for disease and insect damage are one of the most important issues. In particular, agricultural chemicals have become essential members for the current agriculture for ensuring food production, for example, for the measures for disease and insect damage, the use of such as herbicides for work saving, the use for stabilizing the quality or yield, and so on. However, by considering the use of agricultural chemicals for killing insects and bacteria, their toxicity against humans is high, and they have a risk of having adverse effects on the health of agricultural producers and consumers. With regard to the restriction on the use of agricultural chemicals, the criteria for use and the like are stipulated in the “Agricultural Chemicals Regulation Law”, however, the present situation is that among agricultural chemicals which are allowed to be used, there are a number of agricultural chemicals which are suspected to have acute toxicity, chronic toxicity, carcinogenicity, teratogenicity, multigeneration genotoxicity and the like.
Further, recently, agricultural chemical residues in agricultural products have become a big issue. In order to prevent pathogen infection of plants, spraying of a bactericide is generally performed. However, disease protection by the generally performed spraying of an agricultural chemical has a lot of problems related to safety such as effects on the human body due to agricultural chemical residues in crops and contamination in the environment. Further, in terms of the effect of agricultural chemicals, there is a problem that once a pathogen penetrates plants, agricultural chemicals cannot exhibit their bactericidal effect any more. As measures for plant diseases alternative to conventional agricultural chemicals, a protection technique which has high safety and is not harmful to the environment such as pyroligneous acid, bamboo pyroligneous acid, sodium bicarbonate, electrolyzed acid water and the like is known. However, it is not sufficient in terms of the effect and cost, and a technique of inhibiting a plant disease which is safe and has a high effect has been demanded. Further, also in fields other than a plant disease, microbiological control by ethanol, hypochlorous acid, electrolyzed acid water, invert soap or the like has been performed, however, it is not sufficient in terms of irritation to human, safety and the like.
Many of the conventional agricultural chemicals directly targets plant pathogenic bacteria such as filamentous fungi and bacteria or harmful insects, however, there are problems such as effects on the human body or ambient environment due to the toxicity of the agents as described above. Accordingly, as a chemical substance that activates the biological defense mechanism inherent in plants thereby to express disease resistance in the whole plant body, probenazole, acibenzolar-5-methyl or the like is used. Induction of systemic disease resistance by the activation of the biological defense mechanism inherent in plants is called systemic acquired resistance (SAR).
As the agricultural chemical with the use of the induction of systemic acquired resistance in plants, probenazole and the like have been in practical use, and in particular, probenazole has a very large market as a disease inhibitor against Pyricularia oryzae. However, there arises a problem that an effect of such an agricultural chemical on diseases other than Pyricularia oryzae is small, therefore, a future preparation has been demanded worldwide. Further, a jasmonic acid derivative or an ethylene preparation has been used for the purpose of fruit maturation or promotion of flowering, however, their range of action is limited.
In recent years, many reports have been published that recognition of foreign substances is involved in the activation of a group of resistance genes in plants, and a factor which is recognized as a foreign substance and induces the resistance gene became called an elicitor. That is, in order to prevent pathogen infection of plants, spraying of a bactericide is generally performed. However, when a pathogenic bacterium penetrates plant body, the plant recognizes it and activates the plant defense system such as the synthesis of phytoalexin, which is an antibacterial substance, and defends by itself. A substance that induces such resistance reaction by activating the plant secondary metabolic system is called an elicitor (Patent Documents 4 and 2, and Non-Patent Document 1). The present inventors found that a rare sugar has an action of enhancing disease resistance in a plant and separately applied for a patent (Patent Document 6). That is, it is a phenomenon in which a rare sugar reacts against a plant and a variety of proteins that impart disease resistance in the plant body are produced, and its application as an agent for enhancing a plant activity, an agricultural chemical which is not harmful to the environment or the like is expanded, therefore, it is a basically important study finding. However, because the plant secondary metabolic system is complicated or activation of an enzyme occurs in a short time, the mechanism of activation of plant defense system by the elicitor has hardly been elucidated so far.
A problem caused by the growth of harmful microorganisms has become a critical issue not only in a field of a plant disease, but also in many fields such as processing plants for fresh food such as precut vegetables, food production plants, medical facilities, living environments involving dew formation or the like and air-conditioning equipment involving Legionella bacteria. For example, an ethanol preparation to be used for food and in food production environment is a bactericide that inhibits the growth of saprophytic bacteria having an unfavorable effect on food and food production environment, however, many of them are a high concentration ethanol preparation which imparts an unfavorable taste or odor to food, irritates eyes or throat of workers engaged in the production processing work or has an effect on hands or skin, therefore, there is a problem with ensuring the work force. Further, for washing precut vegetables, sodium hypochlorite or electrolyzed strong acid water is used. This method does not cost much and has a bactericidal activity, therefore, it is widely used. However, because the odor of chlorine remains in the products, when washing with water is carried out again, the expense increases, and further, there is a concern about atopic dermatitis caused by chlorine and carcinogenicity. Although at present, a demand for precut vegetables is expanded, an edible washing up liquid free of agricultural chemicals, which responds to the needs of consumers, cannot be found.
Patent Document 1: JP-A-8-225404
Patent Document 2: JP-A-2000-319107
Patent Document 3: JP-A-2000-44404
Patent Document 4: JP-A-7-67681
Patent Document 5: JP-A-7-10901
Patent Document 6: JP-A-2004-300079
Non-Patent Document 1: Plant Cell Technology, Vol. 2, Supplement 1, p. 399, 1990